The interrelationship between malignancy and immunity will be studied in a Gross passage A virus-mouse system. This study involves analysis of the leukemogenic process from three different points of view. The first is a study of the virus, its sources, and routes of introduction to the host, its sites of action, and dissemination throughout the host. Attention will also be paid to virus-cell interactions in the thymus and the peripheral nodes during leukemogenesis. Second, a study of the immune responses to virus during leukemogenesis and the impact of the virus on host immune capacities will also be carried out. Potentially the sequence of events which occur between virus introduction and the development of full-blown malignancy will emerge. Since allografting has been found to alter the acceptance patterns of normal syngeneic and autologous skin, attempts to modify tumor growth using allografting will be carried out. Perhaps this method will induce remission or even rejection of malignancy by inducing an enhanced immune response to the allograft powerful enough to affect and overwhelm the tumor as well.